Fuel-vortex interactions for enhanced mixing in supersonic flow

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Abstract

An experimental investigation was conducted to compare the supersonic mixing performance
between a novel aerodynamic ramp injector and a physical ramp injector. The aerodynamic ramp
injector consisted of nine, flush-wall jets arranged to produce multiplicative fuel-vortex interactions
for mixing enhancement in a supersonic main flow. The physical ramp injector was a previously
optimized and tested swept-ramp design. Test conditions included a Mach 2.0 freest ream of air with a
Reynolds number of3.63 x 107 per meter and helium injection with jet-to-freestream momentum flux
ratios of 1.0 and 2.0. Planar-laser Rayleigh scattering and conventional probing techniques including
species composition sampling were employed to interrogate the flow field at several downstream
locations. Results show that with increasing jet momentum, the aero-ramp exhibited a significant
increase in penetration while the physical ramp showed no discernible change. The near-field mixing
of the aero-ramp was superior to that of the physical ramp. At the higher jet momentum, the far-field
mixing of the aero-ramp was comparable to the physical ramp. In all cases, the total pressure losses
suffered with the aero-ramp were less than those incurred with the physical ramp. For both injectors,
the total pressure losses decreased with increasing jet momentum. Finally, an analytical relationship
predicting the Rayleigh scattering intensity as a function of helium concentration, pressure, and
temperature was derived and experimentally validated. It is concluded that these results merit
further studies and parametric optimization of the aero-ramp or similar configurations. It is also
concluded that further studies may be conducted to establish the absolute quantitative nature of
the Rayleigh scattering technique.